Interpretive Summary: The channels of agricultural watersheds often are unstable and prone to erosion. Erosion caused by unstable channel boundaries may threaten agricultural lands as well as critical parts of transportation infrastructure such as bridge supports. Countermeasures to erosion are needed to protect lands and structures adjacent to unstable channels. A laboratory study was conducted using a model stream channel to develop and test new methods to prevent erosion in the vicinity of a bridge support located on a stream bank. A number of types of structures were tested in this study and three of these succeeded in reducing erosion at the foot of the model support by at least 75%. The successful countermeasures work by either diverting the erosive flow away from the structure or by making the area around the abutment more resistant to erosion. Design guidance for the use of two of these countermeasures was included in this report. The third is still experimental. This technology will provide new methods for use by managers to protect structures from erosion in agricultural and other watersheds. Countermeasures of this type provide protection for structures and provide improvements to aquatic environments by reducing the erosion, movement, and deposition of sediment in streams and rivers.

Technical Abstract:
Scour at bridge abutments can cause damage or failure of bridges and result in excessive repairs, loss of accessibility, or even death. To mitigate abutment scour, both clear-water and live-bed laboratory experiments in a compound channel were performed using parallel walls and spur dikes as countermeasures, respectively. In addition, collars were tested under clear-water conditions only. It was found that both parallel walls and spur dikes can efficiently protect the abutment from scour provided that they are properly designed. Design guidelines were discussed for both countermeasures. Preliminary clear-water tests of collars as countermeasures against scour showed some promising results although further tests are needed to determine their efficiency and design parameters.